Observation of van der Waals shielding between ultracold polar molecules in optical tweezers

Ultracold collisions between molecules often lead to rapid loss. Often, the two-body loss rates are observed to be near universal loss rates that are independent of scattering lengths and arise from short-range loss. Previously, two-body loss rates well below the universal limit have been demonstrated through repulsive barriers engineered using strong DC or microwave electric fields. Recently, it has been theoretically predicted that collisions between certain rotational and hyperfine states are shielded due to repulsive van der Waals interactions. Here, we report the first observation of such sub-universal loss rates for CaF molecules trapped in optical tweezers. Notably, we observe suppression of inelastic loss by more than two orders of magnitude. We will also discuss ongoing work exploring elastic collisions in these shielded state combinations. Our results demonstrate that the universal loss in molecules can be circumvented without the use of high DC electric or microwave fields, complementing existing shielding techniques. It also opens prospects for collisionally stable molecular spin mixtures and entangling gates.